The present invention relates to the protection of electrical circuits and, more particularly, to the detection of arcing faults in an arcing fault protection assembly which includes a dual-mode power supply to power up the assembly quickly using an inefficient power mode, and then switch to a more efficient power mode after the second power mode reaches steady state.
The electrical systems in residential, commercial and industrial applications usually include a panelboard for receiving electrical power from a utility source. The power is then routed through protection devices to designated branch circuits supplying one or more loads. These protection devices are typically circuit interrupters, such as circuit breakers and fuses, which are designed to interrupt the electrical current if the limits of the conductors supplying the loads are surpassed. The power connection to the electrical systems is reestablished either by resetting the circuit breakers or by replacing the fuses. If the cause of the overload to the system is not removed before the circuit breaker is reset or the fuse is replaced, the circuit interrupters will again interrupt the electrical current to the system. The circuit interrupters, however, will not detect the power overload until the power supplied to the interrupter reaches steady state. Adjusting the power to increase the time for the circuit to reach steady state will cause the interrupter to overheat.
Typically, ground fault detectors interrupt an electric circuit due to a disconnect or trip condition, such as a current overload or ground fault. The current overload condition results when a current exceeds the continuous rating of the breaker for a time interval determined by the trip current. A ground fault trip condition is created by an imbalance of currents flowing between a line conductor and a neutral conductor which could be caused by a leakage current or an arcing fault to ground.
Arcing faults are commonly defined as current through ionized gas between two ends of a broken conductor or at a faulty contact or connector, between two conductors supplying a load, or between a conductor and ground. Arcing faults, however, may not cause a conventional circuit breaker to trip. Arcing fault current levels may be reduced by branch or load impedance to a level below the trip curve settings of the circuit breaker. In addition, an arcing fault which does not contact a grounded conductor, object or person will not trip a ground fault protector.
There are many conditions that may cause an arcing fault, for example, corroded, worn or aged wiring, connectors, contacts or insulation, loose connections, wiring damaged by nails or staples through the insulation, and electrical stress caused by repeated overloading, lightning strikes, etc. These faults may damage the conductor insulation and cause the conductor to reach an unacceptable temperature.
It is an object of the present invention to provide an arc fault and ground fault detection system that includes a dual-mode power supply to quickly power up the system and allow it to detect faults quickly after power is supplied to the system, i.e., after the system is reset.
Other and further objects and advantages of the invention will be apparent to those skilled in the art from the present specification taken with the accompanying drawings and appended claims.
In accordance with one aspect of the invention, there is provided an arcing fault and ground fault detection system comprising at least one sensor responsive to a current flowing in an electrical circuit for developing a corresponding sensor signal; a fault detector responsive to the sensor signal for detecting arcing faults and ground faults and producing corresponding output signals; a dual-mode power supply connected to the electrical circuit and the detector for supplying a predetermined output voltage to the detector, the power supply having first and second modes with the first mode supplying the predetermined output voltage more quickly than, but drawing more supply current than, the second mode; and switching means for switching the power supply from the first mode to the second mode.
The above summary of the present invention is not intended to represent each embodiment or every aspect of the present invention. This is the purpose of the drawings and detailed description which follow.